How often have you been asked what your dream garage is or, worse, your favourite car?

And how often have you ummed and erred before coming to a totally different conclusion from the one you arrived at last month? It’s a problem, we know.

And it’s the key problem with this test, because we already know that the Bentley Continental GT V8 and the Porsche 911 Carrera 4 GTS are both dream cars – both four-seat, four-wheel-drive, everyday supercars that will lavish you with feelgood comforts or buzz you with adrenalin as you wish.

Deciding which one is better is like trying to find quantifiable reasons why chocolate ice cream might be better than vanilla.

But although it’s tempting to shrug and give up, we don’t do that here at Autocar. We will make that decision. And with that in mind, the real test for me started away from the one-dimensional backdrop of our Cold War runway and out on the B1090.

I went with the Bentley first. Select the more purposeful setting on the adaptive air suspension and eight-speed automatic and revel in the way that the GT punches through corners.

Sure, the weighty body takes a moment to settle, and by the time you’ve reached eight-tenths attitude, you’re getting more than a whiff of understeer. But stick to your line and the Bentley sees its way through with more than a dab of sports car finesse to its mostly GT attitude. You can adjust your angle of attack on the throttle, and the light steering has a delightfully accurate, oily-feeling progression.

Even the pitted road surface doesn’t deter the Bentley from its mission to thrill without frightening, as it sponges up high-frequency ripples and lopes over undulations, amid a gloriously clear V8 soundtrack.

It feels like a proper event, wherever and however you’re driving it, and that feeling is bedded in the impressive engineering just as much as it is in the irresistible draw of this car’s rich styling and finish – a finish that seemingly hasn’t worn much, if at all, in the 22,000 miles and nearly three years that it has been on the road.

So where does that leave the 911? Hardly trailing, that’s for sure. The GTS version of the 911 is our favourite of the Carrera line. It has been hardened without being too hard, exhibits added brashness of style without being too brash and has many of the ‘essential’ items that would cost extra on a standard Carrera S, such as the sports exhaust and Chrono Pack, not to mention a power boost.

So it’s the best of the road-biased 911s. That, surely, makes it about the best £100k sports car without a roll cage? Well, yes. Pretty much. More than anything, it’s the dual nature of the 911 that never fails to evoke shock and awe.

You can sit in miserable traffic in absolute comfort and refinement, apart from an unnecessarily heavy clutch on the seven-speed manual gearbox, and then open it up on the right road and enjoy instant access to the sort of fingertip precision that you’d generally associate with vastly more single-minded sports cars.

Yes, even with optional £558 adaptive dampers and standard 20in alloy wheels, it’s a much more abrupt ride quality than the cushy-feeling Bentley, and it’s certainly hard enough to induce the odd wince over sharp-edged or mid-corner bumps. But the pay-off is that you feel keyed in to its responses.

You know intuitively just how much lock to apply to hit that apex, the precise moment you can feed power back in,and the exact level of pressure you need on the brakes as you go into the corner. It speaks to the soul, the 911, and there’s not a moment where it’s not obvious that it is the more poised, better-handling car here.

Then there’s the engine – that unique, metallic-sounding wail, the addictive building of pace as the needle climbs the rev range. For many, the heady shove of low-down torque you get in the Bentley will be more of a kick to use at normal road speeds, but the elastic, long-revving crescendo of the 911’s motor is the more satisfying in white-eyed driving.

So that’s the two distinctly different characters we’re dealing with. But it’s not just a question of whether you want the pointier-feeling, faster car in the shape of the 911, or the evocative sports-cruiser that the Bentley embodies so brilliantly. There’s money to think about, too.

The Bentley you see here is from the company’s official Pre-Owned service, which doesn’t just mean free coffee and a handshake but also includes an unlimited-mileage, three-year warranty, factory tour and invites to the same Bentley owner events that anyone buying new model would get.

Porsche goes one better, matching the three-year, unlimited-mileage warranty and including three years’ European roadside assistance and half a day’s driving tuition at Silverstone.

The Porsche is also cheaper to service, at £1360 for four years as a basic price, which makes the Bentley’s £95 per month fixed-price set-up look expensive, even if it does bring a certain peace of mind that many buying in this stratosphere will cheerfully pay for.

The used Conti’s biggest financial advantage is, of course, that it has already taken its initial hit of depreciation: £35,000 of it since 2012. This makes it around £5k cheaper to buy initially and, if the crystal ball of value expert CAP is to be believed, it’ll lose a mere £41k next to the 911’s forecasted drop of £53k over three years and 30,000 miles.

All of which means that both promise fair ownership prospects and remarkably similar costs, despite one being new and the other used.

With that reassurance, the maths hasn’t been overly helpful in solving The Question. So which car is better? It’s the Porsche, because nothing else has quite the same remarkable breadth of ability and, on most objective fronts, it is the more accomplished car. But if you were to ask which car I’d take home and live with, I’d take the Bentley.

I’d maybe regret it when I found myself on a really good road with about 500kg more than I wanted, but the rest of the time I’d be feeling smug. Really smug.